Power system



Dec. 6, 1932. 7 E. M. JOHNSON 1,890,329

POWER SYSTEM Filed Jan: 28. 1931 2 Sheets-Sheet '1 Eric m. Johnson,

His Attone De,c. 6,1932. I I E. .M. IJOHN$OII 1,

POWER SYSTEM Filed Jan. 28, 1931 2 Shets-Sheet 2 Inventor-z Eric m. Johnson,

H is Attorney Patented PATENT orriclaz v1remn ncoarona'rron onmaw YORK invention relates, j wherein; power is j su pplied to 'fa load device by amain prime mover fandfalso bya an auxiliary primefmoverwhich is not mounted on the same shaft as the mainfprimernover, Inas'uch. systemsthere maybe a I'lSk of the auxiliaryprime mover and any coupling 'between iitrand themain prime mover beingiexr,

ces'sively overloadedat certain times,l for ex-V ample'rwhen the power output of the main a primefmover is reduced for any; reason :or a when an exceptionally heavy supply of powrer is required bythe common load device,- and the present invention is 1 more particularly concerned with L, the prevention, of such over loadingjit being realized thatthis is essential to enableipowerisystems" ofifthis kind to be j reh-deredisuitable for use in applications such,

as fort-he propulsion of ships where various different operating conditions may bewarequired to be met,i necessitating, considerable I V a variation in the meanspeed jofthe propeller as'well as'reversalof the' directionof rotation of said propeller;

.f Accordingly the invention providesa ersystem ofthe character referredto where in controlling meansflfor varying thespeed i 3 ditions the ratio "of'the load on-the auxiliary I ,primel-mover to the load onthe mamprime mover shall not exceed a determined value. In one arrangement according-to the invention; a (cou lin through I which the] power of the auxiliary prime nover istransmitted to the main shaft is provided of the kind :which permits the velocityratio of theitransmission" to be varied andymeans for varying the velocity ratio of said coupling is operativelyconnected with and 1 dependent f upon the operation ofthe'means for vary ng the power output of the main! engine, thejfcon nection being however adjiistablexk 1 -In the case where thelcoupling consists for exampleof a direct current electric generator -driven by" the auxiliaryengine and adapted crowns SYSTEM Application filed January a ree-m1 1 01mm, and in Great Britain January 30, 1930.

to; deliver power to an electric motor conconsequent speed variation of the motor, the

correlation of the said speed'regulator and rheostat being however adjustable. Accordingto an alternative arrangement, which does not require the employment of a couplingof adjustable velocity ratio be tween the auxiliary prime mover and the "main shaft, but employs a coupling which although having a'substantially fixed velocity ratio possesses some resilience so as to permit of cyclic variations in the speeds of one or both prime movers, such as are found to occur in all reciprocating prime movers,

the speed regulator of the main prime mover is directly connected to the speed regulator of the auxiliary prime mover in an adjustable manners? The means for connecting the speed regulator of the main prime mover with that-of the auxiliary prime mover or with'the change speed mechanism of the adjustable velocity ratio coupling may comprise a main controller or regulating member for the main prime mover and an auxiliary controller or regulating member for the auxiliary prime mover or the variable speedratio coupling thereof. is The two controlling or regulating members are sorelated that movement ofthe main regulating member to reduce the speed of the main primemover alsomoves the auxiliary regulating member to reduce the speed of the gauxiliary prime moveror the speed of the driven member of the coupling with respect to the driving member thereof, the movement of the auxiliary regulating member being effected through the intermediary of a connecting member adjustably arranged in suchmanner as to transmit movement of the 'mainiregulating member to the auxiliary regulating member irrespectively of-"their initial relative position. 7 Meansmay also be posed thereon by the coupling'will be simultaneously reduced, unless it has been PI'BVl? ously reduced by a corresponding amount to the reduction now made in the power of the main prime mover, so that no extra load is thrown onthe auxiliary prime mover. However whenthe main shaft runs below its nor- 1 be'employed in the power plant concerned, the

malspeed due to extra heavy loading'thereof. and the main prime mover is working with its regu'latingvalve fully open, overloading of the auxiliary prime. mover during the com tinuance of that condition must be prevented by adjusting the auxiliary regulating mem ber independently of the main regulating member. If, now, the speed of the main shaft is still further reduced by manipulation of the main regulating member, then in accord ance with the invention the auxiliary regulating memberwill be moved by reason of its connection with the main regulating member so as to prevent overloading of the auxiliary engine, and notwithstanding that independent regulation-of the auxiliary enginehad prevlously beeh'made. y v -While'var1ous formsiof prime moversmay v main .primemover may conveniently consist I of a steam engine :or steam turbine while the gine. As a further example, the mai'n'and auxiliary prime movers may be respectively auxiliary. prime mover may take the form of a steam engine, steam turbine jora Diesel ena. slow speed Diesel engine directly-coupled to the'main shaft and a high speed Diesel engine coupled to the'main'shaft either through aflexible coupling or a variable speed gear ori through a flexible coupling and a variable speed'geanf 1 7 .Various forms "of controlling means may be employed to "carry out the invention and some constructions according thereto willnow" be described byway ofexample.

' and 3, and -Figs..6, 7 Sand 9 show further T In the accompanyingdrawingsFig. 1 is a diagrammatic view of a ship propulsion system embodying my inventiong'Fi'gs. 2 and 3 are front and sideviews of the controlling means shown in Fig. 1; Figs. 4 and 5. are

front and side views of a modified form of controlling 'means'which may be used in place of the controllingrmeans shown in Figs. 2

modifications of controlling meansoperating I an "accordance with my invention WlllCh may i as,

housed in pl'ace 'of the controlling. means s o nin F g- 1.; r y

In the system shown in Fig. 1, power is supplied to the propellerv 1 by a mam prime mover 2 and by an auxiliary prime mover 3. Various ,forms of prime movers maybe used but in drawings the prime movers have been illustrated -as steam, turbines. The main prime mover 2 furnishes its power directly to the, propeller 1 through a shaft 4 and the auxiliaryprime mover 3 furnishes its power to the propeller 1 through an electricalcou- 'pling comprising a generator 5 and a motor 6. The generator 5 is driven by the auxiliary prime mover 3 and'the motor 6 is connected ;-to the propeller l.

The power output of the main primemover.

is controlledby a governor 7, which has been illustrated as havingthe construction of the governor in Emmet Patent =No. 1,137,308 of April 27,1915, although other forms of controlling means may be used. The speed of the auxiliary prime mover 3 is controlled by a governor 8 and the output of this prime mover to'the propeller 1 is controlled by suitably controlling the electrical coupling 5,6. The governor 7 for prime mover 2'i's under the control of a lever 9 which is connected to. the governor actuating rodlO and theelectrical coupling 5, 6 isunder the control of alever 11 WhichmaycOntrOI the excitation of the generator, the motor or the generator and motor. In-the'system illustrated it controls the excitation of the generator 5 through a rheostat 12. Exciting current for the generator and motor issupplied by an exciter13- .7 Y

The rheostat'controll-ing lever 11 is, rotatably mounted upon aface-plate 14=having a number-of fixed contact studs 15 with which a" contact brushldcarrie'd upon said arm is adaptedto: cooperate. 'Movement of the arm 11rin the oneor other direction over the studs is adapted to cause successively increasing or decreasinglamounts of resistance to be inserted in the excitation circuit of the electric. generator '5 so that the operating .speed of the electric motor 6' which is mechanically connected to the main shaft' may be varied between minimum and maximum values in a well known manner. When'the-arm 11 is moved in the-clockwise direction the speed of the motor 6 -is1=reduced-until thearm passes beyond the range of the studs .15 in that direction wherebyv the power supply to the motor willbe entirelycut ofi. I

-The-contact arm 11, which may conveniently be formed of two'parts, as seen inFig. 3,

v carries a sector-shaped-plate 17, the position .of which is adjustable relatively thereto so that more or lessofthe said plate may extend on one side Jof the arm- The plate 1-7 is heldin an adjusted position on the arm by means of aspr'ing detentllS mounted on the arm 11 and adapted to engage any one of a series ofnotches 19 in the plate.

Y .Thelever 9 ,:hereinafterreferredto as the I jection 20 extending into the pathof thesec tor-plate 17, sothatif the regulator "arm is "Tmoved towards the rheostat arm, the projection 20 ultimately comesfinto contact with i the end or a stop 20 at oneend of the sector plate 17 and thus limits the angular position of the one arm withrespect to the other. The a, angle between the two arms' is limited by the length of; the larcuate 1 portion of the sector plate 17 extending on one sidej of the rheostat; arm'll. Further movementoftheiregur; lator arm in the direction to reduce the power output of the main'primemover willbe transmitted'to the rheostat arm when the-projection on the regulator armjcomes into coni i m with the p Carried by therheostat The sector plate 7 17 carries a latch member 21 preferably spring-pressed,vand adaptedto;

engage ;a pin22 on theface-;p1ate 14when the sector plate is moved clockwise by the g rheostat arm into an extreme position beyond that in which the resistanceinthe generator excit'ationcircuit has been raisedto a maximum andfthe motor is l lo longer supplied withpower. Whenthe sectorplate'is in this position and thelatch 21 engages the pin22,

fitlies" wholly beyond the range of the contactstuds 15 so thatto whatever position the rheostat arm: may be moved upon the sector plate, the motor Qwill remain inoperative;

Moreover, in this position of the sector plate,

the regulator arm, if "moved so as to reduce and eventually to cut'ofijthe motive fluid of the prime mover,'willfbring,its proje'ctihn i into, engagement with the end of said plate;

The rheostat arm"11' further carries an abutment=23, which may be brought into con-:

tact withthe latch 21 for' thepurposeof releasing same fromthe'pin 22 by movement of the I rheostat arm '.;to a the extreme end of the sector plateremote from ftheregulator arm.

'It isthereby assured, that; itfthe power supply to the motor'is once out can will be necessaryfor the rheostat arnito be moved tojthe extreme end of it's travel and have' the maximum length of sectorplate between it and'th'e regulatorarm before the sector plate can be releasedfromthe stop seas topermit the rheostatarm being moved over the contact studs and the motor to be reenergized. The latter operation cannot however occur until thefregulatorfarni-Q is moved into a position to admit motive 'fiuidto the main prime'mover. The rheostat armmaythen be" moved until its "sectorengages the projection of the regulatorarm, and if the do tent ,18 be released the arm may be moved relatively to "the contactstuds "and the length of" the sector extending between :the .contactarm and the'regulatorfarm"may be adjusted until the electrical jmachi'neryis loaded to the required degree according to the prevailing operating conditions. While these same conditions obtain, movement of the regulator arm to reduce speed will be accompanied by corresponding movement of the rheostat arm, while movement :of the regulatorarm to increase speedmaybe followed if desired by a limited movement of the rheostat arm as determined by theefiective length of the sector plate. a e a The stops 2O, 24, carried by the sector plate 17 limit the total amount of movement which may be given to the rheostat arm relative to said plate. The arrangement of the sector plateris preferablysuch thatthe fricficient to hold itin position with respect to said arm when the detent is disengaged from theassociated notches. The friction may be increased by spring pressure if desired In some cases 1t maybe preferred to assomate the rheostat arm with the speed regulator of the prime mover, not directly as iary prime mover. This may be provided for by causing the reversing control mechanism of the mam prime mover to actuatemeans for dlsconnectmg the coupling between the auxiliary prime mover and the load in passing from the forward or ahead to'the reverse or astern position. Such means may be operated by a continuation of the motion g vmg speed regulation of the auxiliary prime mover or of the coupling, or they may comprise separate disconnecting apparatus operated in a known manner from the reversing gear of the mainprime mover. The connection between the reversing control mechanisin and the coupling may be such that the coupling is not reestablished automatically when the said mechanism is returned to the forward position. 7

The apparatus constructed as above described may be readily adapted for this purposef Thus, for example, in the case where reversing control of the main prime mover is a continuation of speed control on theoppositeside of the zero point the arrangement shown in Figs, 4. and 5'may be employed.

These figures show partsof the apparatus illustrated in Figs. 2 and 3 modified for the purpose in view. The regulator arm 9 which is shown partlybroken-away in Fig. 4c is mounted excentrically with the contact arm '11 (not shown) and sector plate 17- instead oi coaxially therewith. The sector plate 17 is provided with apin' 25 adapted't'o engage the 'tion between it and-the rheostat arm is suf'- speed control, but obtainedyfyrom another indicate the extreme position taken up by the 7 no power is then supplied to the motor.

projecting lug 26v on'the regulator arm 9; The; profile of the lug-"26 is formed as shown-atv 27 so as to facilitate its disengagement from the pin'25 as the rheostat arm approa hes its off position. The hatched portions of Fig. 4.

show the lugandpin in ,the'positio'n in which they are about to disengage. The broken lines sector plate 17 when the latch 21 engages the pin 22. In this position the contact maker passes out of engagement with studs and The regulator arm 9iis connected to the throttle valve 28 which controls the supply reversing heels in F ig.:4:. The entire mechanism is so dis-- ofsteam to the forward and reversing wheels =ofthe',:main" prime mover 29 shown in this figure. When the lever arm 9 occupies a posi-' tion where 111g 26 attains'the position shown by the hatched linessteam is cut oil from-both the forward and reversing wheels. of'the' prime: mover. Further movement of arm 9 in a clockwise direction supplies steam to the p of the prime mover for reverse operation; y I

It will be clear from a'comparison of Figs; 4 and 5' with Figs.2 and 3 that whatever may be the'temporary relative positions of the rheostat arm'll and sector 17, the rheostat arm will always have reached its off position at least when the regulatorarm 9 has at-' tained an angular position indicated approximately by the hatched position of the lug- 26 posed with reference to the various positions not take place until the regulator arm has (forward and reverse) ofthe regulatonarm that reversal of the main prime mover will been moved in the clockwise direction beyond the hatched position of the lug 26' above re,-

ferredto. 'Y j I It is preferable that there should be a definite overlap at :thisstage and that in consequence the-motor will-'be deenergi-zed, that is, the coupling between the auxiliary primemover and the main shaft will be disconnected before the main primemover is fully unloaded.

' "In-cases-where the i'reversing control of the mam prime move-r;-1s.,nota continuation of mechanism, provision of thekind referred to will not benecessary. If, howeverfnomterlock is provided between the speedfcontrol' andreversing control of the mainfprime mover to ensure that the speed control is re'- turned to the off position before reve'rsalcan take place (and at the same time consequently to ensure that the coupling is disconnected by its control being simultaneously returned to theiofi position "as previously described) then provision may be made to-connect the regulator of the couplingor ofthe auxiliary prime mover to the reversing mechanism itself."

3 One; methodbyway-of illustration is shown in Fig. fey, [In this figure it is the rheostat; base plate and 17 the sector plate shown in Figs. 2,, 3, l, and 5. The reversing lever of themain prime mover is shown,gfo r' example, as a-lever 30. This lever is connected to the sector platel7 by means of a connecting rod 31 engaging by a slot 32 with a; pin'33;

on the sector plate 17.

. he length and positionsofthe slot are so selected that whatever the position of the sector plate it is always returned to the same position shown in broken lines when the regulating reversing lever 30 is moved from the position marked 0, which is the zero or oif? position, to the position ma'rkedR, which is the reverse or asternvposition. The final position of sector 17 v is such that even when the rheostat arm has. beenrotated as far as possiblein a counter-clockwisei direction upon the sector plate, the rheostat arm (not shown in Fig. 6) willfinally be in its zero or off position before the reversing lever 30 reaches;

the position for reverse or astern running.

An. alternative construction for efiecting the desired control of themotor-generator coupling in accordance with the operation of the speed regulator of the main prime mover may utilize two rheostats, one associated with the'regu'lator arm of the main prime mover soa s to be movable in accordance therewith substantially as above described, and the other being independently adjustable. Such construction preferably includes interlocking means to ensure thatthe operating arm of the independently adjustable rheostat cannot be I movedfrom the oiflposition unless the arm of the otherrheostat is in a position where further movement is limited by the regulator arm, and'further thelast mentioned rheostat arm cannot be moved from the fofi-positionunless the first'mentioned rheostat arm is also in the ofii position. 7 if In the construction which .will now be described. the auxiliary prime mover is provided with two controls in series (for example two rheostats for an electrical coupling or two throttle valves for a prime mover) and full power cannot be vobtained unless both these controls are in the full on position and power is cut off if either of the controls is returned to the off position.

Such an arrangement is illustrated by way of example in Figs. 7 and 8 of thedrawings in which 34 and 35 are two rheostats, and 36 the regulator arm ofthe main prime mover.

heLarm fimoving'innni on withe in Rheostat 34 is thus driven ator 36 to reduce the speed of the main prime mover, as in the arrangements already described, produces an appropriate reduction in the load on the auxiliary prime mover through the medium of rheostat 34, and if.

- continued far enough willeventually also move rheostat 35 towards its off position so that the next time the plant is loaded up.

power cannot be put on the auxiliary prime 35. a a i It will be understood that instead of regu- 'lating the motor-generator coupling by means of one or more rheostats in the generator excitation circuit as described 'ln'the above example, resistance inthemotor field circuit for example, or inboth generator and motor field circuits maybe employed for this a purpose if desired, the controlling apparatus being modified accordingly. a

A similar controlarrangement canbe used for the direct control of the auxiliary prime mover through the medium of the two valves which may be connected together and to the regulator of the main prime mover in a similar mannerto that shown in Figs. 7 and 18, or through'other forms of connection, for example, gearing, in an equivalent manner. Other methodsof connecting the two rheostats and'the regulatorarmmay also be employed provided the relations described in connection with Fig. 6 are maintained.

As] pointed out above an alternative arrangement may be provided in which the speed regulator of the main prime mover is directly connected to the speedregulator of theauxiliary prime moverinan adjustable manner. One way of obtaining this connectionis shown in Fig. 9 of the drawings. The rarrangementoffparts illustratedin Fi .9 is essentially the same as that shown in igs. 2 and 3, exceptthat the rheostat arm 11 becomes a regulating arm ll for controlling the speed of the auxiliary prime mover. The regulator arms 9 and 11 are respectively connected to the throttles or governors of the main and auxiliary prime movers through lsuitable mechanical connections indicated in. the drawings. The correspondence of parts in the arrangement shown in F ig. 9 to that shown in Figs. 2 and3 is apparent andlike "reference numerals have been applied to like arts; As in the arrangement illustrated in igs. 2 and 3,"the arrangementin Fig. 9

mover except under the control of rheostat the auxiliary source relative to the main source through the agency of the sector plate 17 and the stops 20 and 21. The operator by setting arm 9 to a predetermined position may determine the speed of the main prime mover.

Thereafter, by operating arm 11 the speed ofthe auxiliary prime mover may be adjusted but due to stops 20 and 20 the speed of the auxiliary primemover cannot be increased above a predetermined value determined by thesetti'ng of the plate 17 relative to arm 11 This setting also prevents the operator decreasing the speed and power output of the mainprime mover relative to the speed and power output of the auxiliary prime mover below a predetermined ratio since after this ratio has been attained movement of arm 9 also causes simultaneous movement of arm 11'.

.In cases where it is desired to control the -1 operation'of the prime mover from a number of different places, for example, by controlling a throttle valve and also the boiler fans, apparatus of the character above described may be provided at each point of control. In such case the resistances of the two rheostats or sets of rheostats may be connected inseries and arranged so that the full power cannot be obtained. unless both rheostats or sets of rheostats are in the full on position, while movement of any one of the rheostats towards the off position will produce the desired change in theelectrical system.

It will be apparent from the foregoing de scription that the invention provides means, whereby the loading of the main and auxiliary. prime movers may be apportioned in a a desired mannerand the load ,on the main prime mover may be varied while maintainmg that on the auxiliary prime mover con: stant or while varying it also in a predetermined manner,'the risk of excessively overloading the auxiliary prime mover being substantially eliminated.

sired, arran ed and protected against the risk of overloading substantially as hereinbefore indicated.

The invention may employ various forms ofresilient or flexible couplings as well as couplings of adjustable velocity ratio between the auxiliary prime mover and the load be- 1 sides the electrical form of coupling hereinbefore mentioned, and various other modifications may be made without departing from theinvention.

What I claim as new and desire to secure by Letters Patent of the Unitedv States, is: a 1. A power system comprising a main source of power, an auxiliary source of power, a load device common to both of said power sources, means for controlling the out- "put of said main source of power, means for controlling the out ut of said auxiliary "sonrceo-f power, an means associated with both of said controlling means for setting the maximum power output of said auxiliary source relative vto said main source.

9;. A power system comprising a vmain source of power, an auxiliary source of power, a load device common to both of power sources, means including a lever for -Controlling theoutpu-t to said main source of power, means including a lever for controlling the output of said auxiliary source of M power, and an adjustable stop device associ- "-ated with one of said levers and extending *in the pat-hot movement of the second of said levers ior'liniiting the maximum power output of said auxiliary source of. power rela- I tive to said main source of power. 7 3. 'A power system comprising a main source or power, an: auxiliary source of power, a load device common to of said power sources, means for controlling the output-of said main source of power, mean for source of power,- and means 'for setting the maximum power output position of said auxjilia'ry controlling means for any given power 7 position of said main controllin means and rer simultaneously operating said auxiliary *controlling means toward its off-position when said main oontrollingmeans is moved toward its -ofi-position below said given power p'osit'i 011.. r

" ;4. A power system comprising *a main source or power, an auxiliary source of powena load'd'evice common to both of said power-sources, means for controlling the out- "power output position of said auxiliary controlling means for any given powerposition of said main controlling means and for simul- 'tsneously'opera 'ting said auxiliary controlli means toward'i-ts ofi-position when saidmain "controlling means is moved to a po ition below said given power position, means for lockingsaid lastsmentionedmeans in the position its off-position, and means associated with "said auxiliarypower controlling ineai-is for; unlocking said means when 'Sald auxiliary source of ower, an auxiliary source ofpower,-a load devicecommon to both or said a power sources, means for controlling, the directionof rotation and amount of'power 'supplied by said main source of power to "said load device, and means responsive to said last-mentioned means for interrupting fth'esupp lyof power from said auxiliary source of power to said load device before I plurality of devices arranged in series with one another so that movement of either of means for connecting said main controlling (a means to one of said devices for simultaneous i;

operation therewith, and means connected to and operated by said main controlling means of said main source of power, means for :controlling the output ofsaidauxili a ry source "of power, means for setting the maximum I it assumes when the main control means is in i propelleran auxiliary prime mover, a genappease said main controlling means is moved toa position for reverse operation of said main "source of power. I 6. A power system compris ng a" main source of power, an auxiliary source 015750 power, a load device colnmonto both of said power sources, means for controlling the direction of rotation and amount of'power supplied by sa-i'd'main source to said load means and for-simultaneously decreasing the output ofsa' id auxiliary source with s'al'd main source when the controlling means for said main source is operated beyond saida?! given position-toward its off-position, said -me'ans bein-g'inoperative after said auxiliagv ontrolling device has been moved to its 0 V position- I control-ling the output of said auxiliary v source ofpower, an auxiliary source of power,

:7. A power system"'comprising a main 59 a load device common to-both of said power sources, 'means for -c'ontrolling' the output of said main source of power, means, lncluding a said devices to its oil-position reduces the outputof said'auxiliary prime mover to zero, for

propeller, a. main'prime mover for driving said propeller, an electric motor for driving I,

said propeller, an auxiliary prime mover,

a 'g'eneratordriven by said auxiliary prime mover, means for electrically coupling said generator and said motor, means for controllingthe power output of said main prime mover, means for controlling the power cou pling between said generator and said motor, and means associated with said controlling means for limiting the maximum amount of power supplied through said electrical coupling to said propeller for any given positfion of "said main controlling means and for decreasing the power supplied through said coupling and when said main controlling means is moved toward its ofi'-position beyond said given position.

9. In a ship propulsion system, a propeller,

-a main prime mover for driving said propeller, an electric 'motor for driving said erator driven-bysaid auxiliary prime mover,

' theoutput of said main prime mover to said "means for electrically connecting said generator and said motor, means for controlling propeller, means for controlling the power outputof said auxili'aryprime mover through said generator and motor to said propeller, a I

stop device attached to one of said controlling means and extending into thepath of movement of the other 0 for limiting the movement of one of said controlling means toward the other of said con trolling means and for setting the power position of the controlling means associated with said auxiliary prime mover for any given power position of the controlling means i associated with said mainfprime mover.

10. In a ship, propulsion system, a propeller, a main prime mover for driving said propeller, an electric motor, for driving said propeller, an auxiliary prime mover, a generator driven by saidauxiliary prime mover, means for electrically connecting said generator and saidmotor, means for controlling the output of said main prime mover to said propeller, means for controlling the power ,output of said auxiliary prime mover through said generator and motor to said propeller, a stop device associated, with and adjustable relatively to the controlling means for said auxiliary prime mover extending into the path of movement of the controlling means for said main prime mover for operating said auxiliary controlling means by said main controlling means when it is moved to its ofi-position, means for locking said stop device in the position it assumes when said main controlling means is 1n 1ts off-position, and means associated with said auxillary controlling device for unlocking said stop dev1ce when sald auxiliary control means is moved to its extreme off-position.

i In witness whereof I have hereunto set my hand this 14th day of J anuary,1931.

" ERIC JOHNSON.

said controlling means 

